Contemporarily there are two types of pocket wheels for imparting pull on a chain trained thereover, as the wheel is rotated. In one, the periphery of the wheel is provided with successive pockets which respectively receive a link lying parallel to the axis of wheel rotation and a link lying perpendicular to such axis. Such a construction is employed in the Burrows U.S. Pat. No. 3,266,331 of Aug. 16, 1966.
The other type is the so-called "oblique lay" pocket wheel in which the pockets are so disposed that successive links lie at an angle to the center plane of the wheel. Such a construction is exemplified by the Herman U.S. Pat. No. 325,534 of Sept. 1, 1885 and the Crowe patent 662,768 of Nov. 27, 1900. In these patents, the links lie at approximately 45.degree. to the center plane so that successive links still lie in perpendicular planes when passing over the wheel. In a recent development as shown in the Royer et al U.S. Pat. No. 3,415,135, assigned in common herewith, an angle of lay considerably less than 45.degree. was proposed in order materially to reduce the onset of chain link fatigue.
In the conventional type of pocket wheel as exemplified in the patent first mentioned, two types of oscillatory loads are imposed upon the chain as the wheel is rotated. One oscillatory load is due to the entering (or leaving) of a loaded link into a parallel pocket of the wheel and the other oscillatory load is due to the entering (or leaving) of a loaded link into a perpendicular pocket of the wheel. In an oblique lay wheel, each link leaves or enter its pocket in the same way so that only one type of oscillatory load is imposed on the load system. Whereas the oscillatory load can become very large due to resonance in either system, it is easier to control and to minimize oscillatory loading in an oblique lay system. Moreover, the bending stresses induced in the links as they enter or leave a pocket of a correctly designed oblique lay wheel can be reduced.